1. Field of the Invention
The present invention relates to a wiring structure of a semiconductor device and a production method of the device.
2. Description of the Related Art
With progress of miniaturization of the semiconductor device, influence of RC delay (signal delay caused by resistance and capacitance) becomes serious, or becomes a great reason that hinders speed-up of the device operation. To reduce the resistance of the wiring and interconnect capacitance, wiring using copper Cu instead of an aluminum alloy is introduced in a semiconductor device having a wiring width of 0.25 μm or less. Since dry etching is generally difficult in formation of the wiring using Cu, the Damascene method, in which Cu is deposited into grooves for wiring formed on an insulating film and then planarized, is used.
In the formation of the Cu wiring using the Damascene method, the grooves for wiring are formed on a first insulating film, then a barrier film for preventing Cu diffusion and a Cu wiring film are deposited in order in the grooves, and then surfaces are planarized using the chemical mechanical polishing (CMP) method, and the Cu wiring film and the barrier film are left in the grooves. Subsequently, a cap film comprising silicon nitride SixNy is deposited on the Cu wiring film. This is because Cu is easily oxidized and thus a silicon oxide film can riot be directly deposited on the Cu wiring film, therefore the Cu wiring film needs to be covered by the silicon nitride film. However, when an insulating film such as the SixNy is used as the cap film, adhesiveness between the cap film that is the insulating film and the Cu wiring film that is a metal film is bad, and electromigration is apt to occur at a boundary surface between the cap film and the Cu wiring film. Therefore, a method in which the Cu wiring film is selectively coated by a metal film such as CoWP or CoWB film instead of covered by the insulating film is proposed.
The wiring structure in which the Cu wiring film is coated by the metal film is, for example, described in the patent literature 1. In this wiring structure, the barrier film and the Cu wiring film are embedded in the grooves for wiring formed on the first insulating film, then a conductive film (cap film) containing cobalt Co or nickel Ni as a main component is selectively formed on the Cu wiring film by electroless plating, and then CoxSiyPz or NixSiyPz is deposited on the cap film by the electroless plating and made into silicide, thereby an oxidation prevention film is formed.
A wiring structure in which diffusion of Cu ions or spreading of Cu hillocks due to the electromigration are restrained is described in the patent literature 2. In the wiring structure, although the Cu wiring films are embedded in the grooves for wiring on the first insulating film via the barrier films, the Cu wiring films and the barrier films are formed protrusively above the grooves. A cap film comprising an insulating film such as silicon carbide SixCy is formed on an entire surface such that the cap film covers the Cu wiring films and the barrier films protruded from the grooves for wiring. In the wiring structure, top edges of the Cu wiring films that are leakage sources of the wiring material are separated vertically from boundary faces of the first insulating film that are leakage current paths.                PATENT DOCUMENT 1        JP-A-2003-179000 (FIG. 1 on page 5)        PATENT DOCUMENT 2        JP-A-2002-329780 (FIG. 20 on page 15)        
In the wiring structure described in the patent literature 1, the top edges of the Cu wiring films that are the leakage sources of the wiring material are close to the boundary faces of the first insulating film that are the leakage current paths through boundary faces between the cap film and the barrier films, and the Cu ions easily reach the leakage current paths through the boundary faces between the cap film and the barrier films, and thus the leakage current may flow into the adjacent Cu wiring films.
In the wiring structure described in the patent literature 2, although the top edges of the Cu wiring films that are the leakage sources of the wiring material are separated vertically from the boundary faces of the first insulating film that are the leakage current paths, since the cap film formed on the Cu wiring films is an insulating film, adhesiveness at the boundary faces between the Cu wiring films and the cap film or at the boundary faces between the barrier films and the cap film is bad. The electromigration is apt to occur on the tops of the Cu wiring films due to the bad adhesiveness at the boundary faces between the Cu wiring films and the cap film, and when influence of the electromigration is large, the Cu ion's or the Cu hillocks may reach the boundary faces of the first insulating film that are the leakage current paths from the top edges of the Cu wiring films through the boundary faces between the barrier films and the cap film at which the adhesiveness is bad, resulting in increase of the leakage current or an interconnect short-circuit.